Jordan wrote:

i.e. what changes are happening as an engine ages/wears
that increases vibration/shake?


Ignition might be less effective on older engine (missing "bangs"
leading to more shakes)?
Something out of balance? I had a blade come off the fan at speed on a
truck once - the resulting vibration was astonishing.

When a Diesel misses, it produces HUGE clouds of white smoke (oil mist)
out the
exhaust. Also, by the sound, you will definitely know something is
really wrong.
Due to the much greater noise of the combustion in the cylinder, when it
misses,
that little silence really stands out.

Jon